1. Field of the Invention
The present invention relates to a method and apparatus for producing flexible flat containers made of substantially plastic material, sterilizable and capable of containing a liquid to be maintained and extracted under absolutely sterile conditions. These containers consist of a liquid containment body formed of walls made of material thermo-sealed on at least two sides, and of a valve element through which pointed means for removal of liquid can penetrate. This valve element may be made of a rubber piece coated with a plastic material.
2. Statement of the Prior Art
Flat flexible containers provided with an element for defluxion or liquid removal are already described in the technical literature. In particular, U.S. Pat. No. 2,704,075 describes flat flexible containers consisting of a containment body (an envelope or bag) constructed from tubular plastic material sealed at its ends, and of an element (e.g., rubber or plastic resilient material) which may be obtained as a continuous rib on the tubular containment body during extrusion, or applied by welding on the tubular containment body's wall. The element may be sealed in a plastic envelope made of PVC or polyethylene. The envelope containing the element has edges of the PVC or polyethylene protruding beyond the perimeter of said element. Generally, this last element is attached to the container or is kept sterile by a piece of Scotch tape which is removed at the moment of use.
The containers according to this prior (1952) patent have not, to date, had commercial success; in fact, the patented article has not been used on a commercial or even an experimental basis.
Containers similar to those of the above U.S. patent are described in the French Patent Publication No. 2,186,402 (filed May 29, 1973, with the priority of May 30, 1972); here too, the indicated bag forming material is PVC or polyethylene. There are no examples of commercial application in the market place. The scarce commerical use of flat flexible containers in the field of sterile liquids, particularly of perfusion solutions, seems substantially due to problems with the indicated materials, PVC or polyethylene. Indeed, it is very difficult to make bags (with or without valves) which are sterilizable by common means (e.g., vapor) at temperatures above 110.degree. C. Moreover, and especially with regard to PVC, contamination of the liquids contained in the bags by the decomposition products of the film-forming polymeric blend (above all, chloro-vinyl copolymer, plasticizer) is a persistent problem. Furthermore, PVC is highly permeable to water vapor and absorbs medicinal substances which renders it useless in many applications. Efforts to substitute film or sheets of PVC or polyethylene with films or laminates based on other polymers or copolymers (e.g., requiring substantially no plasticizers) have been severely limited not only in the very nature of these materials (none of which shows singularly the required combination of properties) but above all in the difficulty of providing them with a valve device satisfactorily fulfilling the three requirements of easy applicability, sure holding, and an absolute lack of contaminating decomposition products.